title: Osteoblastoma of the sacrum: report of 18 cases and analysis of the literature.
abstract: METHODS
  Retrospective case series.
  
  
  OBJECTIVE
  (1) To analyze clinical and radiographical characteristics, treatment, and outcome in patients with sacral osteoblastoma, (2) to evaluate progression-free survival and local recurrence rate, and (3) to identify prognostic factors.
  
  
  BACKGROUND
  Osteoblastoma is a rare tumor that has been reported to affect the sacrum from 7% to 17%. Symptoms are various and the diagnosis is often delayed.
  
  
  METHODS
  From 1980 to 2010, 18 patients with sacral osteoblastoma (16 males and 2 females) were treated at Rizzoli Institute. Lesion involved S1 (2 cases), S1-S2 (3 cases), S2 (1 case), S2-S3 (1 case), S2-S4 (1 case), S3 (2 cases), S3-S4 (5 cases), S4 (1 case), and almost the entire sacrum in 2 cases. According to Enneking classification for benign bone tumors, 13 (72%) were diagnosed at stage 2 and 5 (28%) at stage 3. Mean tumor volume was 64 cm (range, 2-441 cm). Nine patients had preoperative magnetic resonance imaging. Five patients had a previous inadequate intralesional surgery elsewhere. Treatment consisted in intralesional surgery (16 cases), intralesional surgery and radiotherapy (1 case), and wide resection (1 case). Local adjuvants used were phenol (7 patients), cryocoagulation with "iceball" technique (1 case). Embolizations were performed in 7 patients.
  
  
  RESULTS
  At a mean of 8.4 years (range, 1-28 yr), 15 patients (83%) remained continuously disease free, whereas 3 patients had local recurrence (17%). Progression-free survival was 87% at 5 years and 74% at 10 years. No statistical difference was found between patients who received or not local adjuvants (P = 1.254), older or younger than 20 years (P = 0.970), at stage 2 or 3 (P = 0.826), evaluated preoperatively with or without magnetic resonance imaging (P = 0.160), primarily treated versus patients with previous intralesional surgery elsewhere (P = 0.131).
  
  
  CONCLUSIONS
  In our series, curettage was successful in most of the patients. Local adjuvants did not seem to reduce the risk of local recurrence when combined with intralesional surgery.
  
  
  METHODS
  4.
authors.affiliation: *Department of Orthopedics, University of Bologna, Istituto Ortopedico Rizzoli, Bologna, Italy †Department of Orthopaedic Surgery, University of Ulm, Ulm, Germany; and ‡Department of Radiology, Catholic University, Rome, Italy.
authors.forename: Pietro
authors.initials: P
authors.lastname: Ruggieri
authors.forename: Klaus
authors.initials: K
authors.lastname: Huch
authors.forename: Andreas F
authors.initials: AF
authors.lastname: Mavrogenis
authors.forename: Biagio
authors.initials: B
authors.lastname: Merlino
authors.forename: Andrea
authors.initials: A
authors.lastname: Angelini
mesh_terms: D000293:Adolescent; D000328:Adult; D001859:Bone Neoplasms / Q000175:diagnosis* / Q000601:surgery*; D002648:Child; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D018215:Osteoblastoma / Q000175:diagnosis* / Q000601:surgery*; D012447:Sacrum / Q000473:pathology* / Q000601:surgery; D055815:Young Adult